Short-term recovery of urban soil functions after de-sealing in Palermo (Italy)

Urban soil sealing impairs stormwater regulation, microclimate and biological activity, yet field evidence on how newly de-sealed soils evolve in Mediterranean cities remains scarce. We report a 24-month experiment in Palermo (Italy) on a long-sealed parking-lot Technosol where asphalt was removed and four surface treatments were compared: two unvegetated crushed-asphalt options and two vegetated soil-rehabilitation treatments with imported topsoil. We monitored steady-state Beerkan infiltration, soil cone penetrometer resistance, vegetation dynamics, CO2 efflux, microbial loads and spectral properties relative to conditions one week after de-sealing (time 0). Immediately after asphalt removal, all plots showed extremely high infiltration, typical of structureless coarse rubble. By 18 months, steady-state infiltration had declined by 25-97% relative to the initial measurement and diverged among treatments: vegetated rehabilitation plots exhibited the strongest proportional reductions and longest run times, while unvegetated crushed-asphalt surfaces retained much higher infiltrability. Cone resistance in previously compacted sublayers fell by around an order of magnitude relative to pre-de-sealing values, approaching ranges favourable for root growth. Vegetation established more rapidly and densely in rehabilitated plots, which also showed higher microbial loads and CO2 efflux than crushed-asphalt surfaces and sealed controls, indicating rapid reactivation of soil biological functioning. Surface albedo increased relative to asphalt as vegetation developed, suggesting co-benefits for local heat-stress mitigation. Overall, our results show that micro-de-sealing can transform sealed rubble into functional soil-plant systems within a few years, but hydrological and biological trajectories depend strongly on surface design and vegetation choice.